Microwave energized plasma lamp with solid dielectric waveguide

Abstract

A plasma lamp including a waveguide body consisting essentially of at least one dielectric material having a dielectric constant greater than approximately 2. The body is coupled to a microwave power source which causes the body to resonate in at least one resonant mode. At least one lamp chamber integrated with the body contains a bulb with a fill forming a light-emitting plasma when the chamber receives power from the resonating body. A bulb either is self-enclosed or an envelope sealed by a window or lens covering the chamber aperture. Embodiments disclosed include lamps having a drive probe and a feedback probe, and lamps having a drive probe, feedback probe and start probe, which minimize power reflected from the body back to the source when the source operates: (a) at a frequency such that the body resonates in a single mode; or (b) at one frequency such that the body resonates in a relatively higher order mode before a plasma is formed, and at another frequency such that the body resonates in a relatively lower order mode after it reaches steady state.

1. A lamp comprising:
 (a) a waveguide having a body of a preselected shape and preselected dimensions consisting essentially of at least one solid dielectric material, the body having a first side determined by a first waveguide outer surface;  
 (b) a lamp chamber depending from said first side and having an aperture at said waveguide outer surface generally opposed to a lamp chamber bottom, the waveguide body and lamp chamber comprising an integrated structure;  
 (c) a first microwave probe positioned within and in intimate contact with the waveguide body, adapted to couple microwave power into the body from a source of microwave power having an output and an input and operating at a preselected frequency and intensity, the probe connected to the source output, said frequency and intensity and said body shape and dimensions selected such that the waveguide body resonates in at least one resonant mode having at least one electric field maximum; and  
 (d) the lamp chamber containing a fill mixture consisting essentially of a starting gas and a light emitter, the fill mixture when receiving microwave power at said frequency and intensity, provided by the resonating waveguide body, forming a plasma which emits light.  
 
     
     
       2. The lamp of  claim 1 , further comprising:
 means for depositing the starting gas and light emitter within the lamp chamber; and  
 means for sealing the aperture to the external environment, thereby sealing the lamp chamber to said environment while allowing transmission of light from the lamp chamber.  
 
     
     
       3. The lamp of  claim 1 , further comprising a self-enclosed bulb disposed within the lamp chamber and containing said fill mixture. 
     
     
       4. The lamp of  claim 2  or  3 , further comprising a second probe disposed within the waveguide body, the first and second probes positioned anywhere except near a minimum of the electric field resulting from the source operating at a frequency such that the waveguide body resonates in a single resonant mode, the second probe connected to said source input thereby forming an oscillator configuration maintaining the first probe such that power reflected from the waveguide body back to the source is minimized. 
     
     
       5. The lamp of  claim 2  or  3 , further comprising a second probe disposed within the waveguide body, the source operating at a first frequency such that the waveguide body resonates in a relatively higher order resonant mode before the plasma is formed, and at a second frequency such that the waveguide body resonates in a relatively lower order resonant mode after the plasma reaches a steady state, the first probe disposed near an electric field minimum of the higher order mode and not near an electric field minimum of the lower order mode, the second probe disposed anywhere except near an electric field minimum of the higher order mode or the lower order mode, the second probe connected to said source input thereby forming an oscillator configuration maintaining the first probe such that power reflected from the waveguide body back to the source is minimized both before the plasma is fanned and after the plasma reaches said steady state. 
     
     
       6. The lamp of  claim 2  or  3 , further comprising a second probe and a third probe each disposed within the waveguide body anywhere except near a minimum of the electric field resulting from the source operating at a frequency such that the waveguide body resonates in a single resonant mode, the second probe connected to said source input and the third probe connected to said source output through a phase shifter and a splitter, thereby forming a configuration maintaining the third probe such that power reflected from the waveguide body back to the source is minimized before the plasma is formed, and maintaining the first probe such that power reflected from the waveguide body back to the source is minimized after the plasma reaches a steady state. 
     
     
       7. The lamp of  claim 2  or  3 , further comprising: a second probe and a third probe each disposed within the waveguide body anywhere except near a minimum of the electric field resulting from the source operating at a frequency such that the waveguide body resonates in a single resonant mode; and
 a circulator having interconnected first, second and third ports, the first probe connected to said second port, said first port connected to said source output, the second probe connected to said source input, and said third port connected to the third probe, thereby forming a configuration maintaining the third probe such that power reflected from the waveguide body back to the source is minimized before the plasma is formed, and maintaining the first probe such that power reflected from the waveguide body back to the source is minimized after the plasma reaches a steady state.  
 
     
     
       8. The lamp of  claim 2  or  3 , further comprising a second probe and a third probe each disposed within the waveguide body, the source operating at a first frequency such that the waveguide body resonates in a relatively higher order resonant mode before the plasma is formed, and at a second frequency such that the waveguide body resonates in a relatively lower order resonant mode after the plasma reaches a steady state, the first probe disposed near or at an electric field minimum of the higher order mode and not near an electric field minimum of the lower order mode, the second probe disposed anywhere except near an electric field minimum of the lower order mode or the higher order mode, the third probe disposed anywhere except near an electric field minimum of the higher order mode, the first and third probes connected to said source output through a diplexer which separates said first and second frequencies, the second probe connected to said source input, thereby maintaining the first and third probes such that power reflected from the waveguide body back to the source is minimized both before the plasma is formed and after the plasma reaches said steady state. 
     
     
       9. The lamp of  claim 2  wherein:
 said means for sealing the aperture comprises a window sealed to said first waveguide outer surface in an inert atmosphere, using a ceramic seal; and  
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp chamber bottom having a first hole therethrough;  
 the waveguide having a second body side generally opposed to said first waveguide body side and having a second hole extending in a tapped bore through the waveguide body terminating in said first hole;  
 the waveguide body positioned within an atmospheric chamber containing the starting gas at or near a preselected lamp non-operating pressure;  
 the light emitter deposited in the lamp chamber through said bore and first hole; and  
 a plug screwed into said bore.  
 
     
     
       10. The lamp of  claim 2  wherein:
 said means for sealing the aperture comprises a window sealed to said first waveguide outer surface in an inert atmosphere; and  
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp chamber having a lower portion tapering in a neck terminating in a second aperture;  
 the waveguide having a second body side generally opposed to said first waveguide body side and having a second hole extending in a tapered bore through the waveguide body in communication with the neck, forming a lip;  
 the waveguide body positioned within an atmospheric chamber containing the starting gas at or near a preselected lamp non-operating pressure;  
 the light emitter deposited in the lamp chamber through said second hole, bore and second aperture; and  
 a plug fitted into said bore so that the plug contacts said lip, effecting a mechanical seal.  
 
     
     
       11. The lamp of  claim 9  or  10  wherein a material is deposited over said plug head to effect a final seal. 
     
     
       12. The lamp of  claim 10  wherein said plug comprises a tip adapted to extend within the lamp chamber, thereby creating a discontinuity which provides an electric field concentration point. 
     
     
       13. The lamp of  claim 2  wherein:
 said means for sealing the aperture comprises a window sealed to said first waveguide outer surface in an inert atmosphere; and  
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp chamber bottom having a first hole therethrough;  
 the waveguide having a second body side generally opposed to said first waveguide body side and having a second hole extending in a bore through the waveguide body in communication with said first hole;  
 a tube having an end and made of a first dielectric material inserted through said second hole and into said bore so that said tube end extends through said first hole into the lamp chamber;  
 a fill mixture of starting gas and light emitter deposited into the evacuated lamp chamber via the tube; and  
 a rod made of a second dielectric material inserted into the tube.  
 
     
     
       14. The lamp of  claim 13  wherein said first and second dielectric materials are each selected from the group consisting of glass and quartz. 
     
     
       15. The lamp of  claim 2  wherein:
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp chamber having a side with a first hole;  
 said first waveguide body side having a second hole in communication with said first hole;  
 a tube having an end and made of a first dielectric material inserted through said first and second holes so that said tube end penetrates the lamp chamber;  
 a fill mixture of starting gas and light emitter deposited into the evacuated lamp chamber via the tube; and  
 a rod made of a second dielectric material inserted into the tube; and  
 said means for sealing the aperture comprises a window sealed to said first waveguide outer surface at a temperature which will not melt said tube.  
 
     
     
       16. The lamp of  claim 15  wherein said first and second dielectric materials are each selected from the group consisting of glass and quartz. 
     
     
       17. The lamp of  claim 2  wherein:
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp positioned within an atmospheric chamber containing the starting gas at a pressure at or near the non-operating lamp pressure, and the light emitter deposited in the lamp chamber; and  
 said means for sealing the aperture comprises:  
 first and second clamps attached to said first waveguide body side;  
 said first waveguide body side having an O-ring groove circumscribing said aperture; and  
 a window and an O-ring pre-positioned within the atmospheric chamber, the O-ring disposed within said groove, the window covering said aperture, the clamps tightened so as to bring the window into pressing contact with the O-ring and said first waveguide outer surface.  
 
     
     
       18. The lamp of  claim 2  wherein:
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp positioned within an atmospheric chamber containing the starting gas at a pressure at or near the non-operating lamp pressure, and the light emitter deposited in the lamp chamber; and  
 said means for sealing the aperture comprises:  
 the lamp further comprising generally opposed first and second portions generally orthogonal to said first waveguide body side and extending, respectively, in first and second upper portions each having an interior surface with a thread engaging a screw-type cap with a central hole therethrough;  
 said first waveguide body side having an O-ring groove circumscribing said aperture; and  
 a window and an O-ring pre-positioned within the atmospheric chamber, the O-ring disposed within said groove, the window covering said aperture, the cap screwed so as to bring the window into pressing contact with the O-ring and said first waveguide outer surface.  
 
     
     
       19. The lamp of  claim 2  wherein:
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp positioned within an atmospheric chamber containing the starting gas at a pressure at or near the non-operating lamp pressure, and the light emitter deposited in the lamp chamber; and  
 said means for sealing the aperture comprises:  
 said first waveguide body side having a detail circumscribing said aperture and adapted to closely receive a seal preform;  
 a window and a seal preform pre-positioned within the atmospheric chamber, and the seal preform placed in the detail;  
 the window positioned on top of the seal preform, and the waveguide body in thermal contact with a cold surface; and  
 a hot mandrel in pressing contact with the window.  
 
     
     
       20. The lamp of  claim 2  wherein:
 said means for depositing the starting gas and light emitter within the lamp chamber comprises:  
 the lamp positioned within an atmospheric chamber containing the starting gas at a pressure at or near the non-operating lamp pressure, and the light emitter deposited in the lamp chamber; and  
 said means for sealing the aperture comprises:  
 said first waveguide body side having a detail circumscribing said aperture in which is disposed a first metallization ring and a seal preform superposed on said ring; and  
 a window having a lower surface to which is attached a second metallization ring, the window positioned on top of the seal preform so that the seal preform is sandwiched between the first and second metallization rings while heating means is applied to melt the seal preform.  
 
     
     
       21. The lamp of  claim 20  wherein said heating means is selected from the group consisting of a brazing flame, a laser, and a radio frequency coil. 
     
     
       22. The lamp of  claim 1 , wherein an optical element is rigidly attached to a heatsink which closely receives the waveguide body, and said element is generally aligned with said lamp chamber aperture. 
     
     
       23. The lamp of  claim 22  wherein said optical element is selected from the group consisting of a lens, a light pipe, and a tube lined with a reflective material. 
     
     
       24. The lamp of  claim 1 , wherein said waveguide body has a generally cylindrical shape and is received within a generally cylindrical bore of a generally cylindrical metallic heatsink. 
     
     
       25. The lamp of  claim 24  wherein a compliant, high temperature, thermal interface material is interposed between the waveguide body and heatsink. 
     
     
       26. The lamp of  claim 1 , wherein said waveguide body has a generally cylindrical shape and is enclosed by first and second semi-cylindrical portions of a clamshell-type heat sink. 
     
     
       27. The lamp of  claim 4 , further comprising:
 a PIN diode attenuator connected to said feedback probe; and  
 an RF power detector connected to said drive probe;  
 the lamp further comprising a circuit having an amplifier portion comprising a plurality of stages connected between the PIN diode attenuator and RF power detector, and a control portion connected to the PIN diode attenuator, the RF power detector, and an optical power detector.  
 
     
     
       28. The lamp of  claim 27 , wherein said amplifier portion comprises:
 (a) a high power amplifier stage connected to the RF power detector;  
 (b) a medium power amplifier stage connected to the high power amplifier stage; and  
 (c) a preamplifier stage connected between the medium power amplifier stage and the PIN diode attenuator.  
 
     
     
       29. The lamp of  claim 27 , wherein said control portion acts in combination with said PIN diode attenuator to provide a low power mode in which the plasma is maintained at a power level insufficient for light emission but sufficient to keep the fill mixture ionized. 
     
     
       30. The lamp of  claim 27 , wherein said control portion acts in combination with said PIN diode attenuator to shut down the lamp slowly so as to limit thermal shock to the lamp and promote easier lamp starting. 
     
     
       31. The lamp of  claim 27 , wherein said control portion acts in combination with said PIN diode attenuator and said RF power detector to maintain a desired power level during lamp operation, even if the incoming power supply voltage changes due to variation in the power supply output. 
     
     
       32. The lamp of  claim 27 , wherein said control portion acts in combination with said PIN diode attenuator to control the output power at a high level during the early part of the lamp operating cycle, thereby vaporizing the fill mixture more quickly than can be achieved at normal operating power. 
     
     
       33. The lamp of  claim 27 , wherein said control portion acts in combination with said PIN diode attenuator and said optical power detector to maintain a preselected illumination level should power conditions and lamp emission characteristics change. 
     
     
       34. The lamp of  claim 5 , further comprising:
 a PIN diode attenuator connected to said feedback probe; and  
 an RF power detector connected to said drive probe;  
 the lamp further comprising a circuit having an amplifier portion comprising a plurality of stages connected between the PIN diode attenuator and RF power detector, and a control portion connected to the PIN diode attenuator, the RF power detector, and an optical power detector.  
 
     
     
       35. The lamp of  claim 34 , wherein said amplifier portion comprises:
 (a) a high power amplifier stage connected to the REF power detector;  
 (b) a medium power amplifier stage connected to the high power amplifier stage; and  
 (c) a preamplifier stage connected between the medium power amplifier stage and the PIN diode attenuator.  
 
     
     
       36. The lamp of  claim 34 , wherein said control portion acts in combination with said PIN diode attenuator to provide a low power mode in which the plasma is maintained at a power level insufficient for light emission but sufficient to keep the fill mixture ionized. 
     
     
       37. The lamp of  claim 34 , wherein said control portion acts in combination with said PIN diode attenuator to shut down the lamp slowly so as to limit thermal shock to the lamp and promote easier lamp starting. 
     
     
       38. The lamp of  claim 34 , wherein said control portion acts in combination with said PIN diode attenuator and said RF power detector to maintain a desired power level during lamp operation, even if the incoming power supply voltage changes due to variation in the power supply output. 
     
     
       39. The lamp of  claim 34 , wherein said control portion acts in combination with said PIN diode attenuator to control the output power at a high level during the early part of the lamp operating cycle, thereby vaporizing the fill mixture more quickly than can be achieved at normal operating power. 
     
     
       40. The lamp of  claim 34 , wherein said control portion acts in combination with said PIN diode attenuator and said optical power detector to maintain a preselected illumination level should power conditions and lamp emission characteristics change. 
     
     
       41. The lamp of  claim 5 , further comprising:
 a PIN diode attenuator connected between said feedback probe and a first PIN diode switch;  
 a circuit comprising an amplifier portion comprising a plurality of stages connected between a second PIN diode switch and said drive probe, and a control portion connected to the PIN diode attenuator, the first and second PIN diode switches, and an optical power detector; and  
 first and second bandpass filters connected in parallel to the first and second PIN diode switches, the filters independently selectable and switchable by the control portion.  
 
     
     
       42. The lamp of  claim 41 , wherein said amplifier portion comprises:
 (a) a high power amplifier stage connected to said drive probe;  
 (b) a medium power amplifier stage connected to the high power amplifier stage; and  
 (c) a preamplifier stage connected between the medium power amplifier stage and said second PIN diode switch.  
 
     
     
       43. The lamp of  claim 41 , wherein said control portion acts in combination with said first and second PIN diode switches, said first and second bandpass filters, and said PIN diode attenuator to:
 (a) operate the lamp only in that cavity mode corresponding to a preselected frequency band, so all amplifier portion power is directed into this mode;  
 (b) enable a first cavity mode for starting the lamp;  
 (c) enable a second cavity mode once the fill mixture gas has ionized and plasma has begun to form, so that the first and second cavity modes propagate through said waveguide body to ensure that the fill mixture remains a plasma; and  
 (d) shut down the first cavity mode so that only the second mode, preselected for lamp operation, propagates.  
 
     
     
       44. The lamp of  claim 8 , further comprising:
 a PIN diode attenuator connected to said feedback probe;  
 an RF power detector connected to said drive probe;  
 a bipolar PIN diode switch connected to said start probe; and  
 a filter connected to the PIN diode attenuator;  
 the lamp further comprising a circuit having an amplifier portion comprising a plurality of stages including a high power amplifier stage connected between the filter and the RF power detector, and a control portion connected to the PIN diode attenuator, the PIN diode switch, the high power amplifier stage, the RF power detector, and an optical power detector.  
 
     
     
       45. The lamp of  claim 44 , wherein said amplifier portion further comprises:
 (a) a medium power amplifier stage connected between the PIN diode switch and high power amplifier stage; and  
 (b) a preamplifier connected between the filter and PIN diode switch.  
 
     
     
       46. The lamp of  claim 44 , wherein said control portion acts in combination with said PIN diode attenuator, PIN diode switch, filter, RF power detector, and optical power detector to:
 (a) send power to said start probe, which is critically coupled when the lamp is off, until the fill mixture becomes ionized;  
 (b) route power to said high power amplifier stage once the gas becomes ionized; and  
 (c) remove power to the start probe when a predetermined condition is met, so that the plasma is powered only by the drive probe.